verifyPow function
void
verifyPow()
Implementation
void verifyPow() {
final x = Tensor.fill([1, 1], 0.0);
x.data = [3.0];
final loss = x.pow(2.0).sum(); // x^2
loss.backward();
final grads = x.grad;
// d(x^2)/dx = 2x. For x=3, grad = 6.0
bool ok = closeEnough(grads[0], 6.0);
print("POW: ${ok ? '✅ PASS' : '❌ FAIL (Expected 6.0, got ${grads[0]})'}");
}